add: getTemplate option extendDefaults

Author: sagold

README.md

@@ -268,6 +268,32 @@ expect(myData).to.deep.equal({
 
 </details>
 
+<details><summary>Option: extendDefaults</summary>
+
+Per default, `getTemplate` does try to create data that is valid to the json-schema. Example: array-schemas with `minItems: 1` will add one item to fullfil the validation criteria. You can use the option and pass `{ extendDefaults: false }` to override this behaviour with a default value:
+
+```ts
+import { Draft07 } from "json-schema-library";
+
+const myJsonSchema = {
+    type: "array",
+    default: [], // if omitted will add an array item
+    items: {
+        type: "string",
+        enum: ["one", "two"]
+    },
+    minItems: 1 // usually adds an enty, but default states: []
+};
+
+const jsonSchema = new Draft07(myJsonSchema);
+const myData = jsonSchema.getTemplate(undefined, undefined, { extendDefaults: false });
+
+expect(myData).to.deep.equal([]);
+```
+
+</details>
+
+
 ### each
 
 `each` iterates over each data-item (_object_, _array_ and _value_) and emits the data-item, schema and location to a callback.

lib/getTemplate.ts

@@ -15,8 +15,14 @@ import { mergeSchema } from "./mergeSchema";
 export type TemplateOptions = {
     /** Add all properties (required and optional) to the generated data */
     addOptionalProps?: boolean;
-    /** remove data that does not match input schema. Defaults to false */
+    /** Remove data that does not match input schema. Defaults to false */
     removeInvalidData?: boolean;
+    /** Set to false to take default values as they are and not extend them.
+     *  Defaults to true.
+     *  This allows to control template data e.g. enforcing arrays to be empty,
+     *  regardless of minItems settings.
+     */
+    extendDefaults?: boolean;
 };
 
 const defaultOptions: TemplateOptions = {
@@ -257,7 +263,7 @@ const TYPE: Record<
     ) => {
         const template = schema.default === undefined ? {} : schema.default;
         const d: Record<string, unknown> = {}; // do not assign data here, to keep ordering from json-schema
-        const required = schema.required ?? [];
+        const required = (opts.extendDefaults === false && schema.default !== undefined) ? [] : (schema.required ?? []);
 
         if (schema.properties) {
             Object.keys(schema.properties).forEach((key) => {
@@ -345,7 +351,7 @@ const TYPE: Record<
 
         const template = schema.default === undefined ? [] : schema.default;
         const d: unknown[] = data || template;
-        const minItems = schema.minItems || 0;
+        const minItems = (opts.extendDefaults === false && schema.default !== undefined) ? 0 : (schema.minItems || 0);
 
         // build defined set of items
         if (Array.isArray(schema.items)) {

test/unit/getTemplate.test.ts

@@ -1279,5 +1279,74 @@ describe("getTemplate", () => {
 
             expect({ list: [], author: "jane" }).to.deep.equal(template);
         });
+
+
+        describe("extendDefaults", () => {
+
+            it("should keep array default-value with 'extendDefaults:false'", () => {
+                draft.setSchema({
+                    type: "array",
+                    default: [],
+                    items: {
+                        type: "string",
+                        enum: ["one", "two"]
+                    },
+                    minItems: 1 // usually adds an enty, but default states: []
+                });
+                const res = getTemplate(draft, undefined, draft.getSchema(), {
+                    extendDefaults: false
+                });
+
+                expect(res).to.deep.equal([]);
+            });
+
+            it("should add items to array with no default-value given and 'extendDefaults:false'", () => {
+                draft.setSchema({
+                    type: "array",
+                    items: {
+                        type: "string",
+                        enum: ["one", "two"]
+                    },
+                    minItems: 1 // usually adds an enty, but default states: []
+                });
+                const res = getTemplate(draft, undefined, draft.getSchema(), {
+                    extendDefaults: false
+                });
+
+                expect(res).to.deep.equal(["one"]);
+            });
+
+            it("should not add required items to object with default-value given and 'extendDefaults:false'", () => {
+                draft.setSchema({
+                    type: "object",
+                    required: ["title"],
+                    default: {},
+                    properties: {
+                        title: { type: "string" }
+                    }
+                });
+                const res = getTemplate(draft, undefined, draft.getSchema(), {
+                    extendDefaults: false
+                });
+
+                expect(res).to.deep.equal({});
+            });
+
+            it("should extend object by required property with no default-value given and 'extendDefaults:false'", () => {
+                draft.setSchema({
+                    type: "object",
+                    required: ["title"],
+                    properties: {
+                        title: { type: "string" }
+                    }
+                });
+                const res = getTemplate(draft, undefined, draft.getSchema(), {
+                    extendDefaults: false
+                });
+
+                expect(res).to.deep.equal({ title: "" });
+            });
+        });
+
     });
 });